Various types of filters are known for filtering water and similar liquids. A particularly useful type of filter is a disk filter. Filters of this type are described and claimed, for example, in applicant's U. S. Pat. No. 4,624,785; U.S. patent application Ser. No. 709,371, filed Mar. 7, 1985; U.S. Pat. No. 4,683,060, which is now abandoned; U.S. Pat. No. 4,654,163; and U.S. Pat. Nos. 4,026,806; 4,042,504; 4,045,345; 4,271,018; 4,278,540; 4,295,963.